The present disclosure relates to the additive manufacturing arts, three-dimensional printing arts, filter arts, optical arts, coating arts, and the like.
Additive manufacturing (AM) is a new production technology for the rapid and flexible production of prototype parts, end-use parts, and tools using three-dimensional (3D) computer aided design (CAD) models. AM functions to add thin layers between 16 microns and 180 microns of material at a time to create an object. AM produces three-dimensional solid objects of virtually any shape from a digital model. Generally, this is achieved by creating a digital blueprint of a desired solid object with CAD modeling software and then slicing that virtual blueprint into very small digital cross-sections or layers. Each layer begins with a thin distribution of powder, such as metal powder, over the surface of a bed or platform. The powder is selectively joined where the object is to be formed. A piston that supports the bed or platform within a build box lowers so that the next powder layer can be spread over the previous layer and selectively joined. This sequential layering process repeats within an AM machine (such as a three-dimensional printer) to build up the desired part. Unbound powder is removed, and the NNS fabricated part or coated part can be further treated.
AM has many advantages, including dramatically reducing the time from design to prototyping to commercial product. Demonstration units and parts can be rapidly produced. Parts can be created of any geometry, and generally out of any material, including ceramics, metals, polymers, and composites. Local control can be exercised over the material composition, microstructure, and surface texture. Modifications and customizations are possible. Multiple parts can be built in a single assembly. No complicated potentially one-time die or tooling needs to be made before a prototype can be produced. Minimal energy is needed to make these three-dimensional solid objects. It also decreases the amount of waste and raw materials. AM also facilitates the production of extremely complex geometrical parts. Support material can be used to create overhangs, undercuts, and internal volumes. AM also reduces the parts inventory for a business since parts can be quickly made on-demand and on-site.
Three conventional AM methods include electron beam melting, laser beam melting, and laser sintering. In electron beam melting, after the deposition of a powder layer, the loose powder cross-section is melted or fused by an electron beam. Similarly, in laser beam melting, a laser is used to melt or fuse the material being deposited, which can be in the form of a loose powder deposition or fed as a powder or wire while the layers are formed. In laser sintering, a laser beam is used to sinter areas of the loosely compacted powder cross-section. The term “sintering” refers to the process by which particulates adhere into a solid mass, eliminating porosity while maintaining itself in a solid state, due to externally applied energy. These methods will also fuse a given cross-section with the already sintered or melted cross-section beneath. The metal powder that is not struck by the electron or laser beam remains loose and falls away from the finished part when removed from the AM machine. Alternatively, the part can be depowdered by vacuuming, by compressed air, or by a fluid to wash the completed part and dislodge any loose powder. Subsequent finishing steps may also be applied to the part to produce the characteristics desired. Such steps include, but are not limited to, further heat treatment, curing, sintering, annealing, and final surface finishing.
It should be noted that the above-mentioned AM methods each involve heat, and form the object on a base platform that is a part of the printer/AM manufacturing device itself. With the use of heat treatment to sinter or otherwise cure the object, the use of these types of AM methods is limited. A possible solution to the use of heat in the AM manufacturing process is another method involving photopolymerisation.
Photopolymerisation is a technique that involves the solidification of photo-sensitive resin by means of an ultraviolet (“UV”) light. Photopolymerization is used by different three-dimensional printing processes such as three-dimensional Digital Light Processing (DLP), Stereolithography (SLA), and other inkjet-type printers. SLA uses a vat of photopolymer resin that can be cured. The build plate moves down in small increments and the liquid polymer is exposed to light where the UV laser draws a cross section layer by layer. The process repeats until a model has been created. The object is three-dimensional printed by pulling the object out of the resin (bottom up) which creates space for the uncured resin at the bottom of the container and can then form the next layer of the object. Another way is to three-dimensional print the object by pulling it downward into the tank with the next layer being cured on the top. These photopolymer parts do not have the strength of SLS or FDM parts, but can typically achieve much higher levels of detail. As the photopolymer is UV sensitive, these products are susceptible to deforming and changing colors in sunlight. SLA is commonly used to generate highly detailed artwork, non-functional prototypes, and can be used to make molds in investment casting applications).
In DLP, a projector is used to cure photopolymer resin. The DLP AM method is substantially similar to SLA, wherein instead of a UV laser to cure the photopolymer resin, a safelight (light bulb) is used. Objects are created the same as SLA with the object being either pulled out of the resin which creates space for the uncured resin at the bottom of the container and to form the next layer of the object or down into the tank with the next layer being cured on the top.
Objects that are printed with Digital Light Processing have less visible layers versus other processes such as FDM/FFF. Compared with SLA, DLP can have faster build speeds due to a single layer being created in one singular digital image whereas with SLA, the UV laser has to scan the vat with a single point (trace out the object layer). Also, the same photopolymer resins that can be used with SLA can be used for DLP three-dimensional Printing. Objects printed with this process have the same strengths and weaknesses. Similar to SLA, DLP is commonly used to generate highly detailed artwork, non-functional prototypes, and can be used to make molds in investment casting applications.
In inkjet-type AM methods, a process similar to stereolithography is employed. Three-dimensional inkjet printers use a UV light to crosslink a photopolymer. However, rather than scanning a laser to cure layers, a printer head jets tiny droplets of the photopolymer (similar to ink in an inkjet printer) in the shape of the first layer. The UV lamp attached to the printer head crosslinks the polymer and locks the shape of the layer in place. The build platform then steps down one layer thickness and more material is deposited directly on the previous layer. This is process is repeated until the part has completed printing. Combining two or three materials in specific concentrations and microstructures (poly-jet three-dimensional printing) allows the production of a range of materials with varying translucency, rigidity, thermal resistance or color. Using this process, a single part can contain materials with diverse physical and mechanical properties ranging from rubber-like flexibility to ABS-like rigidity. Similar to SLA, the photopolymer is vulnerable to sunlight and heat, and the material can creep over time. Poly-jet three-dimensional printing is typically used for developing fully assembled prototypes and complex and detailed geometries with multiple material properties.
Each AM method or process described above, and the printers currently available, all form an object from scratch. That is, none of the processes or devices is currently capable of building upon an existing structure or substrate. Part of the reasons for this are the incompatibility of the materials, the susceptibility of the existing structure to warping or other damage from heat or submersion in materials, the instructions set requiring a flat platform upon which to build, and the like. This problem is exacerbated when dealing with existing structures or substrates that are already coated in films, e.g., optical wafers, filters, etc., and which can react negatively to the application of heat, certain wavelengths of light, and the like.
For example, optical filters with high spectral selectivity are manufactured using a stack of layers, with alternating layers of two (or more) constituent materials having different refractive index values. Such filters may be referred to as interference filters, and can be designed to provide a designed pass-band, stop-band, high-pass, or low-pass output. For pass-band filters, the width of the pass-band can typically be made as narrow as desired by using more layer periods in the stack, albeit possibly with some transmission loss at the peak transmission wavelength. A notch filter can be similarly designed by constructing the stack of layers to form a Bragg reflector blocking the stop-band. The layer stack is deposited on a substrate that is optically transmissive for the wavelength or wavelength range to be transmitted, and may for example be a glass plate for an optical filter operating in the visible spectrum. This results in a filter plate whose structural rigidity is provided by the substrate.
In such optical filters, a given filter plate operates at a single well defined pass band or stop band. The layers of the stack are typically required to have precise thicknesses to meet the specified wavelength and bandwidth for the pass band or stop band.
However, it is difficult or impossible to vary the layer thicknesses across the substrate plate during layer deposition or by post deposition processing in a controlled manner in order to provide different pass bands or stop bands in different areas of the plate. Such an arrangement is useful for a spectrometer, spectrum analyzer, or other “multi spectral” applications.
Filter arrays address this problem by fabricating a set of filter plates with different filter characteristics (e.g. different pass band or stop band wavelength and/or bandwidth). The filter plates are then diced to form filter elements in the form of strips. These strips are then bonded together in a desired pattern to form the filter array. The resulting filter array is sometimes referred to as a “butcher block” due to its similarity in bonding structural elements (filter elements here, c.f. wood elements in the case of an actual butcher block). This approach decouples the optical characteristics of each filter element of the filter array from those of the other filter elements, enabling substantially any combination of filter elements in a single filter array.
Currently, aperture masks are deposited in a similar fashion as the optical coatings themselves. The aperture masks are deposited using a photolithographic process and an optical coating. A chemical compound is applied to the filter array or wafer in a design corresponding to the desired aperture. This forms a mask on the wafer, masking away those portions that are to remain. An etching compound is then applied, which removes the non-masked portions of the wafer. The mask is then removed via application of a suitable chemical leaving the aperture mask formed on the wafer.
Furthermore, some of these optical components employ microstructures, which require additional instructions to the printer as to where to deposit the materials for printing, especially for those microstructures having different heights to which the printer must adapt without damaging the underlying substrate. It would be desirable to have systems and methods that allow for printing coatings onto an optical wafer that eliminate the aforementioned problems while implementing the advantages of additive manufacturing processes.